Dr Stuart Butchart of BirdLife International and colleagues used data on birds to estimate the financial costs of meeting these targets.

They sampled 211 globally threatened bird species and asked experts to estimate the cost of preserving these from extinction.

The researchers then extrapolated this to the cost of protecting the 1115 globally threatened bird species and the cost of protecting all known threatened species globally.

"Threatened birds comprise 7.65 per cent of all threatened species on the global IUCN Red List suggesting that the total annual costs of conserving all 'known threatened species' ... may range from $3.41 billion ... to $4.76 billion," the researchers write.

The researchers also found it would cost US$76.1 billion annually to meet the target of managing and expanding protected areas to cover 17 per cent of terrestrial and in-land water areas (and 10 per cent of coastal and marine areas).

"Meeting these targets will require conservation funding to increase by at least an order of magnitude," write the researchers, but they add this is small compared to other expenditure.